Anti-tachycardia pacing methods and devices

ABSTRACT

An improved method and device for performing anti-tachycardia pacing (ATP) to convert a ventricular tachycardia (VT) to normal sinus rhythm. Pacing/sensing electrodes are implanted in or on the left and right ventricles of a patient&#39;s heart. After a VT is detected a determination is made based on the shape of the electrogram signal of the VT. One of a plurality of time offsets for pacing pulses of the left and right ventricles is selected based on the signal shape and ATP is performed by pacing both the left and right ventricles with the time offset between pulses in the respective ventricles.

This application is related to copending application Ser. Nos.10/045,495, 10/039,734, 10/045,570, and 10/067,116 all filed on Oct. 19,2001.

FIELD OF THE INVENTION

The present invention relates generally to implantable cardiacstimulation devices. The present invention more particularly relates tomethods and devices for multi-chamber anti-tachycardia pacing.

BACKGROUND OF THE INVENTION

The heart is a series of pumps that are carefully controlled by a veryspecial electrical system. This electrical system attempts to regulatethe heart rate between 60 and 100 beats per minute. The initialelectrical signal originates near the top of the upper chamber on theright side of the heart. This chamber is called the “right atrium” andthe special tissue that generates the signal is called the “sino-atrial”or SA node.

The electrical signal continues in a downward fashion through the“atrio-ventricular” or AV node, where the signal is slowed slightly byspecial tissue. The AV node is the “doorway” or relay station to thebundle of His (pronounced Hiss), and the bundle branches in the lowerchambers of the heart.

After passing through the left and right bundle branches, the impulsearrives at the Purkinje fibers, where it is transmitted to the musclecells of the left and right ventricles. Because of the specialized wayin which the impulse is transmitted, the ventricles contract almostsimultaneously.

With normal conduction, the cardiac contractions are very organized andtimed so that the top chambers (the atria) contract before the lowerchambers and the heart rate is maintained between 60 and 100 beats perminute.

Abnormally fast heart rates are called tachycardias. As used herein, theterm tachycardia means a heartbeat at a rate which is abnormally highand accordingly considered to be dangerous if permitted to continue, orany arrhythmia involving recognizable heartbeat patterns containingrepetitions which are in excess of a periodic heartbeat within a saferange.

When the ventricular chambers beat too quickly, the arrhythmia (i.e.,unusual heart rhythm) is known as ventricular tachycardia. Whenventricular tachycardia (VT) occurs, the ventricles may not be able tofill with enough blood to supply the body with the oxygen rich bloodthat it needs. Symptoms of VT include feeling faint, sometimes passingout, dizzyness, or a pounding in the chest.

Ventricular tachycardia may be controlled by medication in some cases.If medications are not effective, the physician may elect to control therhythm by electrical methods. The most common electrical therapy for VTis implantation of a device known as an Implantable CardioverterDefibrillator (ICD). The ICD applies an electric shock to the heartmuscle to interrupt or disrupt the fast rhythm. The electric shock maybe in the form of specially timed pacemaker pulses (unfelt by thepatient) or by high voltage shock. The high voltage shock, if required,is usually painful to the patient. Accordingly, it is preferential touse pacemaker pulses (also referred to as pacing pulses).

Tachycardias can result due to any number of reasons. For example,patients who have had myocardial infarctions, or other diseases thatcreate scarring in the ventricular region of the heart, often developmonomorphic ventricular tachycardias. A monomorphic ventriculartachycardia (MVT) is a type of tachycardia that originates from oneventricular focus. These tachycardias often arise in and around the areaof scarring on the heart. They are typically uniform and typically occurat a regular rate. Faster MVTs are often associated with hemodynamiccompromise, whereas slower MVTs can be very stable.

Anti-Tachycardia Pacing (ATP) has been used to convert ventriculartachycardias into normal sinus rhythm. However, conventional ATP has notproved to be one hundred percent successful at returning the heart tonormal sinus rhythm. Additionally, in a rare case, conventional ATP willaccelerate the rhythm to ventricular fibrillation. Accordingly, improvedmethods and apparatuses for decreasing the failure rate of ATP arerequired. Some of the prior patent documents which teach ATP using lowvoltage shock therapy systems include U.S. Pat. Nos. 4,408,606,4,398,536, 4,488,553, 4,488,554, 4,390,021, 4,181,133 and 4,280,502.

Tachycardia is often the result of electrical feedback within the heart;a natural beat results in the feedback of an electrical stimulus whichprematurely triggers another beat. By interposing a stimulated heartbeat(i.e., a pacing pulse), the stability of the feedback loop is disrupted.For example, patients with MVT can often times be successfully paced outof the tachycardia using a rapid burst of high rate pacing. The burstconsists of a selected number of pulses all delivered at the same rate,an accelerating rate, or an alternating accelerating/decelerating rate.The mechanism that determines success of the burst is the ability topeel-back the refractories between the pacing site and the origin of thearrhythmia and penetrate the reentrant loop.

In conventional ATP, anti-tachycardia pacing pulses are delivered usingtwo electrodes within the right ventricle (RV). The inventors of thepresent invention are aware of one study of the efficacy ofbi-ventricular (BV) ATP. See Bocchiardo et al., “Efficacy ofBiventricular Sensing and Treatment of Ventricular Arryhthmias,” PACE,Vol. 23, November 2000, pp. 1989-1991. In the Bocchiardo study, the BVpacing was accomplished using an RV tip electrode, an RV proximalelectrode, and an LV tip electrode. The Bocchiardo study concluded that“[t]he success rates of spontaneous VT termination by BV ATP versus RVATP were comparable.” The inventors of the present invention, however,believe that there may be many advantages to BV ATP.

There is a need for improved methods and devices for ATP. Morespecifically, there is a need to increase the success rate (i.e.,decrease the failure rate) of VT termination using ATP. Such improvedmethods and devices will preferably also reduce the amount of timerequired to convert a tachycardia to normal sinus rhythm.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to improved methods and devices forperforming anti-tachycardia pacing (ATP) to convert a ventriculartachycardia (VT) to normal sinus rhythm. Pacing/sensing electrodes areimplanted in or on the left and right ventricles of a patient's heartand are used for sensing a VT and performing ATP.

In a preferred embodiment, one of a plurality of time offsets isselected based on the shape of a signal indicative of the tachycardia.First anti-tachycardia pacing pulses are delivered to the rightventricle and second anti-tachycardia pulses are delivered to the leftventricle. Each pulse in the second pulses is offset in time from acorresponding pulse in the first pulses by the selected time offset.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

Further features and advantages of the present invention may be morereadily understood by reference to the following description taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a simplified diagram illustrating an exemplary implantablestimulation device in electrical communication with at least three leadsimplanted into a patient's heart for delivering multi-chamberstimulation and shock therapy;

FIG. 2 is a functional block diagram of the multi-chamber implantablestimulation device of FIG. 1 illustrating the basic elements of thestimulation device which can provide cardioversion, defibrillation andpacing stimulation in four chambers of the heart;

FIG. 3 illustrates an exemplary waveform corresponding to a far fieldsignal, an exemplary waveform corresponding to a signal sensed in theleft ventricle, an exemplary waveform corresponding to a signal sensedin the right ventricle, an exemplary left ventricle and right ventriclepacing signal;

FIG. 4 is a flowchart describing a method for independent bi-ventricularanti-tachycardia pacing, according to an embodiment of the presentinvention;

FIG. 5 is a flowchart describing a method for anti-tachycardia pacingwhere a pair of electrodes that are determined to be closer to thereentrant loop are used first to deliver pacing pulses, according to anembodiment of the present invention;

FIG. 6 is a flowchart describing a method for unipolar pacing, accordingto an embodiment of the present invention;

FIG. 7 is a flowchart describing a method for changing pacingconfigurations, according to an embodiment of the present invention;

FIG. 8 is a flowchart describing a method for selecting a pacingconfiguration, according to an embodiment of the present invention; and

FIG. 9 is a flowchart describing a method for selecting a time offsetbetween pacing pulses in different chambers of the heart, according toan embodiment of the present invention;

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best mode presently contemplated forpracticing the invention. This description is not to be taken in alimiting sense but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe ascertained with reference to the issued claims. In the descriptionof the invention that follows, like numerals or reference designatorswill be used to refer to like parts or elements throughout.

I. Exemplary Stimulation Device

As shown in FIG. 1, there is a stimulation device 10 in electricalcommunication with a patient's heart 12 by way of three leads, 20, 24and 30, suitable for delivering multi-chamber stimulation and shocktherapy. To sense atrial cardiac signals and to provide right atrialchamber stimulation therapy, the stimulation device 10 is coupled to animplantable right atrial lead 20 having at least an atrial tip electrode22, which typically is implanted in the patient's right atrialappendage. Stimulation device 10 is also known as and referred to as apacing device, a pacing apparatus, a cardiac rhythm management device,or an implantable cardiac stimulation device. Stimulation device 10 canbe an implantable cardioverter/defibrillator (ICD).

To sense left atrial and ventricular cardiac signals and to provide leftchamber pacing therapy, the stimulation device 10 is coupled to a“coronary sinus” lead 24 designed for placement in the “coronary sinusregion” via the coronary sinus os for positioning a distal electrodeadjacent to the left ventricle and/or additional electrode(s) adjacentto the left atrium. As used herein, the phrase “coronary sinus region”refers to the vasculature of the left ventricle, including any portionof the coronary sinus, great cardiac vein, left marginal vein, leftposterior ventricular vein, middle cardiac vein, and/or small cardiacvein or any other cardiac vein accessible by the coronary sinus.

Accordingly, an exemplary coronary sinus lead 24 is designed to receiveatrial and ventricular cardiac signals and to deliver left ventricularpacing therapy using a left ventricular (LV) tip electrode 26 and a LVring 25. Left atrial pacing therapy uses, for example, first and secondleft atrial (LA) ring electrodes 27 and 28. Shocking therapy can beperformed useing at least a left atrial (LA) coil electrode 29. For adescription of an exemplary coronary sinus lead, see U.S. patentapplication Ser. No. 09/196,898, “A Self-Anchoring Coronary Sinus Lead”(Pianca et al.), and U.S. Pat. No. 5,466,254, “Coronary Sinus Lead withAtrial Sensing Capability” (Helland), which patent documents areincorporated herein by reference. Coronary sinus lead 24 can alsoinclude a pair of right atrial (RA) rings 13 and 14 that may be used toprovide right atrial chamber pacing therapy, as shown in FIG. 1.

The stimulation device 10 is also shown in electrical communication withthe patient's heart 12 by way of an implantable right ventricular lead30 having, in this embodiment, an RV tip electrode 32, an RV ringelectrode 34, an RV coil electrode 36, and a superior vena cava (SVC)coil electrode 38 (also known as a right atrial (RA) coil electrode).Typically, the right ventricular lead 30 is transvenously inserted intothe heart 12 so as to place the right ventricular tip electrode 32 inthe right ventricular apex so that the RV coil electrode 36 will bepositioned in the right ventricle and the SVC coil electrode 38 will bepositioned in the superior vena cava. Accordingly, the right ventricularlead 30 is capable of receiving cardiac signals, and deliveringstimulation in the form of pacing and shock therapy to the rightventricle.

FIG. 2 illustrates a simplified block diagram of the exemplarymulti-chamber implantable stimulation device 10, which is capable oftreating both fast and slow arrhythmias with stimulation therapy,including cardioversion, defibrillation, and pacing stimulation. While aparticular multi-chamber device is shown, this is for illustrationpurposes only, and one of skill in the art could readily duplicate,eliminate or disable the appropriate circuitry in any desiredcombination to provide a device capable of treating the appropriatechamber(s) with cardioversion, defibrillation and pacing stimulation.

The housing 40 for the stimulation device 10, shown schematically inFIG. 2, is often referred to as the “can”, “case” or “case electrode”and may be programmably selected to act as the return electrode for all“unipolar” modes. The housing 40 may further be used as a returnelectrode alone or in combination with one or more of the coilelectrodes, 29, 36 and 38 of FIG. 1, for shocking purposes. The housing40 further includes a connector (not shown) having a plurality ofterminals, 44, 45, 46, 47, 48, 52, 54, 56, 58, 59 and 60 (shownschematically and, for convenience, the names of the electrodes to whichthey are connected are shown next to the terminals). As such, to achieveright atrial sensing and pacing, the connector includes, for example, apair of right atrial ring terminals 59 and 60 that are respectivelyadapted for connection to first right atrial (RA) ring electrode 13 andsecond RA ring electrode 14.

To achieve left chamber sensing, pacing and shocking, the connectorincludes, for example, a left ventricular tip terminal 44, a leftventricular ring terminal 45, a pair of left atrial ring terminals 46and 47, and a left atrial shocking terminal 48, which are adapted forconnection to the LV tip electrode 26, the LV ring electrode 25, firstLA ring electrode 27 and second LA ring electrode 28, and LA coilelectrode 29, respectively.

To support right chamber sensing, pacing and shocking, the connectorfurther includes, for example, a right ventricular tip terminal 52, aright ventricular ring terminal 54, a right ventricular shockingterminal 56, and an SVC shocking terminal 58, which are adapted forconnection to the RV tip electrode 32, RV ring electrode 34, the RV coilelectrode 36, and the SVC coil electrode 38 (also know as RA coilelectrode 38), respectively.

At the core of the stimulation device 10 is a programmablemicrocontroller 60 which controls the various modes of stimulationtherapy. As is well known in the art, the microcontroller 60 typicallyincludes a microprocessor, or equivalent control circuitry, designedspecifically for controlling the delivery of stimulation therapy and mayfurther include RAM or ROM memory, logic and timing circuitry, statemachine circuitry, and I/O circuitry. Typically, the microcontroller 60includes the ability to process or monitor input signals (data) ascontrolled by a program code stored in a designated block of memory. Thedetails of the design and operation of the microcontroller 60 are notcritical to the present invention. Rather, any suitable microcontroller60 may be used that carries out the functions described herein. The useof microprocessor-based control circuits for performing timing and dataanalysis functions are well known in the art.

Representative types of control circuitry that may be used with theinvention include the microprocessor-based control system of U.S. Pat.No. 4,940,052 (Mann et. al.) and the state-machines of U.S. Pat. No.4,712,555 (Sholder) and U.S. Pat. No. 4,944,298 (Sholder). For a moredetailed description of the various timing intervals used within thestimulation device and their inter-relationship, see U.S. Pat. No.4,788,980 (Mann et. al.). The '052, '555, '298 and '980 patents areincorporated herein by reference.

As shown in FIG. 2, an atrial pulse generator 70 and a ventricular pulsegenerator 72 generate pacing stimulation pulses for delivery by theright atrial lead 20, the right ventricular lead 30, and/or the coronarysinus lead 24 via an electrode configuration switch 74 (also referred toas switch bank 74). It is understood that in order to providestimulation therapy in each of the four chambers of the heart, theatrial and ventricular pulse generators, 70 and 72, may includededicated, independent pulse generators, multiplexed pulse generators,or shared pulse generators. The pulse generators, 70 and 72, arecontrolled by the microcontroller 60 via appropriate control signals, 76and 78, respectively, to trigger or inhibit the stimulation pulses.

The microcontroller 60 further includes timing control circuitry 79which is used to control the timing of such stimulation pulses (e.g.,pacing rate, atrio-ventricular (AV) delay, atrial interconduction (A-A)delay, or ventricular interconduction (V-V) delay, etc.) as well as tokeep track of the timing of refractory periods, PVARP intervals, noisedetection windows, evoked response windows, alert intervals, markerchannel timing, etc., which are well known in the art.

The switch bank 74 includes a plurality of switches for connecting thedesired electrodes to the appropriate I/O circuits, thereby providingcomplete electrode programmability. Accordingly, the switch 74, inresponse to a control signal 80 from the microcontroller 60, determinesthe polarity of the stimulation pulses (e.g., unipolar, bipolar,combipolar, etc.) by selectively closing the appropriate combination ofswitches (not specifically shown).

Atrial sensing circuits 82 and ventricular sensing circuits 84 may alsobe selectively coupled to the right atrial lead 20, coronary sinus lead24, and the right ventricular lead 30, through the switch 74 fordetecting the presence of cardiac activity in each of the four chambersof the heart. Accordingly, the atrial (ATR. SENSE) and ventricular (VTR.SENSE) sensing circuits, 82 and 84, may include dedicated senseamplifiers, multiplexed amplifiers, or shared amplifiers. The switch 74determines the “sensing polarity” of the cardiac signal by selectivelyclosing the appropriate switches, as is known in the art. In this way,the clinician may program the sensing polarity independent of thestimulation polarity.

Each sensing circuit, 82 and 84, preferably employs one or more lowpower, precision amplifiers with programmable gain and/or automatic gaincontrol, bandpass filtering, and a threshold detection circuit, as knownin the art, to selectively sense the cardiac signal of interest. Theautomatic gain control enables the device 10 to deal effectively withthe difficult problem of sensing the low amplitude signalcharacteristics of atrial or ventricular fibrillation. For a completedescription of a typical sensing circuit, see U.S. Pat. No. 5,573,550,entitled “Implantable Stimulation Device having a Low Noise, Low Power,Precision Amplifier for Amplifying Cardiac Signals” (Zadeh et al.),which is incorporated herein by reference. The outputs of the atrial andventricular sensing circuits, 82 and 84, are connected to themicrocontroller 60 which, in turn, is able to trigger or inhibit theatrial and ventricular pulse generators, 70 and 72, respectively, in ademand fashion in response to the absence or presence of cardiacactivity, respectively, in the appropriate chambers of the heart. Thesensing circuits, 82 and 84, in turn, receive control signals oversignal lines, 86 and 88, from the microcontroller 60 for purposes ofcontrolling the gain, threshold, the polarization charge removalcircuitry (not shown), and the timing of any blocking circuitry (notshown) coupled to the inputs of the sensing circuits,82 and 86, as isknown in the art.

For arrhythmia detection, the device 10 utilizes the atrial andventricular sensing circuits, 82 and 84, to sense cardiac signals todetermine whether a rhythm is physiologic or pathologic. As used herein“sensing” is the receipt or noting of an electrical signal, and“detection” is the processing of these sensed signals and noting thepresence of an arrhythmia. The timing intervals between sensed events(e.g., P-waves, R-waves, and depolarization signals associated withfibrillation which are sometimes referred to as “F-waves” or“Fib-waves”) are then classified by the microcontroller 60 by comparingthem to a predefined rate zone limit (e.g., bradycardia, normal, lowrate VT, high rate VT, and fibrillation rate zones) and various othercharacteristics (e.g., sudden onset, stability, physiologic sensors,morphology, etc.) in order to determine the type of remedial therapythat is needed (e.g., bradycardia pacing, anti-tachycardia pacing,cardioversion shocks or defibrillation shocks, collectively referred toas “tiered therapy”).

Cardiac signals are also applied to the inputs of an analog-to-digital(A/D) data acquisition system 90. The data acquisition system 90 isconfigured to acquire intracardiac electrogram signals, convert the rawanalog data into a digital signal, and store the digital signals forlater processing and/or telemetric transmission to an external device102. The data acquisition system 90 is coupled to the right atrial lead20, the coronary sinus lead 24, and the right ventricular lead 30through the switch 74 to sample cardiac signals across any pair ofdesired electrodes.

Advantageously, the data acquisition system 90 may be coupled to themicrocontroller 60, or other detection circuitry, for detecting anevoked response from the heart 12 in response to an applied stimulus,thereby aiding in the detection of “capture.” Capture occurs when anelectrical stimulus applied to the heart is of sufficient energy todepolarize the cardiac tissue, thereby causing the heart muscle tocontract. The microcontroller 60 detects a depolarization signal duringa window following a stimulation pulse, the presence of which indicatesthat capture has occurred. The microcontroller 60 enables capturedetection by triggering the ventricular pulse generator 72 to generate astimulation pulse, starting a capture detection window using the timingcontrol circuitry 79 within the microcontroller 60, and enabling thedata acquisition system 90 via control signal 92 to sample the cardiacsignal that falls in the capture detection window and, based on theamplitude, determines if capture has occurred.

Capture detection may occur on a beat-by-beat basis or on a sampledbasis. Preferably, a capture threshold search is performed once a dayduring at least the acute phase (e.g., the first 30 days afterimplantation of the ICD) and less frequently thereafter. A capturethreshold search would begin at a desired starting point (either a highenergy level or the level at which capture is currently occurring) anddecrease the energy level until capture is lost. The value at whichcapture is lost is known as the capture threshold. Thereafter, a safetymargin is added to the capture threshold.

The implementation of capture detection circuitry and algorithms arewell known. See for example, U.S. Pat. No. 4,729,376 (Decote, Jr.); U.S.Pat. No. 4,708,142 (Decote, Jr.); U.S. Pat. No. 4,686,988 (Sholder);U.S. Pat. No. 4,969,467 (Callaghan et al.); and U.S. Pat. No. 5350,410(Mann et al.), which patents are incorporated herein by reference. Thetype of capture detection system used is not critical to the presentinvention.

The microcontroller 60 is further coupled to a memory 94 by a suitabledata/address bus 96, wherein the programmable operating parameters usedby the microcontroller 60 are stored and modified, as required, in orderto customize the operation of the stimulation device 10 to suit theneeds of a particular patient. Such operating parameters define, forexample, pacing pulse amplitude, pulse duration, electrode polarity,rate, sensitivity, automatic features, arrhythmia detection criteria,and the amplitude, waveshape and vector of each shocking pulse to bedelivered to the patient's heart 12 within each respective tier oftherapy. A feature of the present invention is the ability to sense andstore a relatively large amount of data (e.g., from the data acquisitionsystem 90), which data may then be used for subsequent analysis toselect, for example, a pacing configuration, as described below.

Advantageously, the operating parameters of the implantable device 10may be non-invasively programmed into the memory 94 through a telemetrycircuit 100 in telemetric communication with the external device 102,such as a programmer, transtelephonic transceiver, or a diagnosticsystem analyzer. The telemetry circuit 100 is activated by themicrocontroller 60 by a control signal 106. The telemetry circuit 100advantageously allows intracardiac electrograms and status informationrelating to the operation of the device 10 (as contained in themicrocontroller 60 or memory 94) to be sent to the external device 102through an established communication link 104.

In the preferred embodiment, the stimulation device 10 further includesa physiologic sensor 108, commonly referred to as a “rate-responsive”sensor because it is typically used to adjust pacing stimulation rateaccording to the exercise state of the patient. However, thephysiological sensor 108 may further be used to detect changes incardiac output, changes in the physiological condition of the heart, ordiurnal changes in activity (e.g., detecting sleep and wake states).Accordingly, the microcontroller 60 responds by adjusting the variouspacing parameters (such as rate, AV Delay, V-V Delay, etc.) at which theatrial and ventricular pulse generators, 70 and 72, generate stimulationpulses.

The stimulation device additionally includes a battery 110 whichprovides operating power to all of the circuits shown in FIG. 2. If thestimulation device 10 employs shocking therapy, then the battery 110must be capable of operating at low current drains for long periods oftime, and then be capable of providing high-current pulses (forcapacitor charging) when the patient requires a shock pulse. The battery110 must also have a predictable discharge characteristic so thatelective replacement time can be detected. Accordingly, the device 10preferably employs lithium/silver vanadium oxide batteries, as is truefor most current devices.

As further shown in FIG. 2, the device 10 is shown as having animpedance measuring circuit 112 which is enabled by the microcontroller60 via a control signal 114. The known uses for an impedance measuringcircuit 120 include, but are not limited to, lead impedance surveillanceduring the acute and chronic phases for proper lead positioning ordislodgement, detecting operable electrodes and automatically switchingto an operable pair if dislodgement occurs; measuring respiration orminute ventilation; measuring thoracic impedance for determining shockthresholds; detecting when the device has been implanted; measuringstroke volume; and detecting the opening of heart valves, etc. Theimpedance measuring circuit 120 is advantageously coupled to the switch74 so that any desired electrode may be used. The impedance measuringcircuit 112 is not critical to the present invention and is shown foronly completeness.

If stimulation device 10 is intended to operate as an implantablecardioverter/defibrillator (ICD) device, it must detect the occurrenceof an arrhythmia, and automatically apply an appropriate electricalshock therapy to the heart aimed at terminating the detected arrhythmia.To this end, the microcontroller 60 further controls a shocking circuit116 by way of a control signal 118. The shocking circuit 116 generatesshocking pulses of low (up to 0.5 joules), moderate (0.5-10 joules), orhigh energy (11 to 40 joules), as controlled by the microcontroller 60.Such shocking pulses are applied to the patient's heart 12 through atleast two shocking electrodes, and as shown in this embodiment, selectedfrom the left atrial (LA) coil electrode 29, the RV coil electrode 36,and/or the SVC coil electrode 38. As noted above, the housing 40 may actas an active electrode in combination with the RV coil electrode 36, oras part of a split electrical vector using the SVC coil electrode 38 orthe LA coil electrode 28 (i.e., using the RV electrode as a commonelectrode).

Cardioversion shocks are generally considered to be of low to moderateenergy level (so as to minimize pain felt by the patient), and/orsynchronized with an R-wave and/or pertaining to the treatment oftachycardia. Defibrillation shocks are generally of moderate to highenergy level (i.e., corresponding to thresholds in the range of 5-40joules), delivered asychronously (since R-waves may be too disorganizedto detect), and pertaining exclusively to the treatment of fibrillation.Accordingly, the microcontroller 60 is capable of controlling thesynchronous or asynchronous delivery of the shocking pulses.

II. Discussion of Tachycardias

Before further explaining the present invention, it is helpful tobriefly review the basic electrophysiologic mechanisms responsible forventricular tachycardias (VTs).

During the normal cardiac cycle, a cardiac cell membrane depolarizes andrepolarizes in a characteristic fashion known as the action potential.Action potential propagation occurs when depolarization in one cellgenerates current to neighboring cells, forcing membrane sodium channelsto open and allowing a rapid excitatory influx of sodium that furtherdepolarizes the membrane. Sodium channels then close. Other ioniccurrents repolarize the membrane to its resting state over a slow timecourse that is sufficiently long for sodium channels to recoverexcitability. Heart rate is important in this process because theinterval between recovery in one cycle and activation in the nextprovides time for the cell to achieve ionic, metabolic and energeticequilibrium.

When cells die in a myocardial infarct, they electrically uncouple fromneighboring viable cells, making the infarct completely inexcitable.Intrinsic or paced wavefronts encountering such an obstacle generallysplit into two components that collide and recombine on the oppositeside of the infarct. When tissue adjacent to the infarct excitesprematurely, however, reentry can result if one of the wavefronts blocksin a region with reduced excitability, i.e. incomplete sodium channelopening. The reduced excitability can result from inhomogeneities inmembrane properties, geometric changes that increase the wavefront'selectrical load, or incomplete recovery of excitability during a shortinterval. When blocking of one wavefront occurs, the other wavefront maybe able to reenter the initial block site, causing was in known as a“reentrant circuit.” Action potentials will continually propagate aroundthe infarct at a rate considerably faster than the heart's intrinsicrate provided the reentrant wavefront, i.e. the head, moves slowlyenough that tissue ahead recovers excitability, i.e. a tail can form.The spatial extent of inexcitable tissue in this circuit is termed thereentrant wavelength, and is approximated by the product of the head'svelocity and the action potential duration. As long as the wavelength isless than the obstacle's perimeter, i.e. the reentrant path length, thehead and tail remain separated by an excitable gap. Termination ofanatomic reentry requires elimination of the excitable gap, which can beachieved by appropriate pacing. An appropriately timed stimulus (i.e., apacing pulse) will initiate action potentials that propagate in bothdirections, colliding with the head and blocking in the tail. One of theobjects of the present invention is to provide improved methods andapparatuses to terminate anatomic reentry.

In more simplified terms, the reentrant circuit can be thought of as aconduction wavefront propagating along a tissue mass of somewhatcircular geometry. This circular conduction will consist of a portion ofrefractory tissue and a portion of excitable tissue. To terminate thecircuit, a pacing stimulas should be provided at the time and locationwhen the tissue just comes out of refractoriness. If this occurs, thepaced stimulation wavefront proceeds toward the advancing wavefront ofthe circuit, colliding with the wavefront and interrupting the circuit.If the pacing stimulus (i.e., pacing pulse) arrives too soon it will beineffective because the tissue will still be in refractoriness. If thestimulas arrives too late, it will generate wavefronts both towards theadvancing wavefront and towards the tail of the circuit. Although onepacing generated wavefront will collide with the advancing wavefront ofthe reentrant circuit and will halt is progress, the latter pacinggenerated wavefront will act to sustain the reentrant circuit.

Accordingly, the probability of ATP succeeding is terminating the VT isrelated to the ability of the pacing stimulation wavefront to arrive atthe location of the reentant circuit (e.g., within a myocardium) in sucha manner that the reentrant circuit is modified or interrupted. Factorsinfluencing this process include the distance of the pacing electrode(s)from the reentrant circuit, the pacing stimulas energy, and the timingof the pacing stimuli relative to the conduction velocities andrefractory periods of the myocardium.

There are several different pacing modalities which have been suggestedfor termination of tachycardia. The underlying principle in all of themis that if a pacing stimuli stimulates the heart at least once shortlyafter a heartbeat, before the next naturally occurring heartbeat at therapid rate, the heart may successively revert to sinus rhythm.Tachycardia is often the result of electrical feedback within the heart;a natural beat results in the feedback of an electrical stimulus whichprematurely triggers another beat. By appropriately interposing astimulated heartbeat, the stability of the feedback loop is disrupted.

III. Overview of the Present Invention

As discussed above, there is a need for improved methods and apparatusesfor decreasing the failure rate of ATP. Referring back to FIG. 1,exemplary pacing device 10 is shown as including many electrodes. In theright ventricle—are the RV coil 36, the RV ring 34 and the RV tip 32. Inthe coronary sinus—are a pair of left atrial (LA) rings 27 and 28, theLV ring 25, and the LV tip 26. In the right atrium is the right atrial(RA) coil 38 and a pair of RA rings 13 and 14. The present inventionuses novel combinations of these electrodes to achieve more effectiveATP. The present invention also uses novel timing schemes to increasethe effectiveness of ATP. The present invention also enables the use ofmultiple different pacing schemes. For example, the present inventionenables the use of multiple different pacing protocols and/or multipledifferent electrode configurations. The present invention furtherprovides for selection of one of multiple different ATP schemes.

IV. Embodiments of the Present Invention

A. Independent Bi-Ventricular Pacing

As mentioned above, there are several different ATP modalities whichhave been suggested for termination of tachycardia, with the underlyingprinciple being to stimulate the heart (i.e., using a pacing pulse) atleast once shortly after a heartbeat, before the next naturallyoccurring heartbeat at the rapid rate, in an attempt to convert thetachycardia to sinus rhythm. In a first embodiment of the presentinvention, pacing pulses are independently produced using a leftventricular (LV) pace/sense electrode pair (e.g., LV ring 25 and LV tip32), and a right ventricular (RV) pace/sense electrode pair (e.g., RVring 34 and RV tip 32). Stated another way, in the first embodiment ofthe present invention, the RV is paced independently from the pacing ofthe LV.

The most common form of ATP is burst pacing, which delivers multiplepacing pulses (i.e., a burst of pulses) at a cycle length between 50 and100% (and more typically between 70 and 90%) of the tachycardia cyclelength. Delivering pulses having, for example, an 80% cycle length, isalso known as delivering pulses having an 80% coupling interval. Eachburst of pacing pulses typically includes 2-20 pulses. The number ofbursts used is typically 1-15. The rate of each burst can either be afixed predetermined rate (i.e., fixed burst) or a rate that iscalculated based on the rate of the VT being treated (adaptive burst).Acceleration risk is minimized by keeping the number of pulses in aburst, the rate of the burst, and the number of bursts to the minimumrequired to terminate the VT. Many ATP regimens employ variations onthis basic theme of burst pacing. As mentioned above, an aspect of thepresent invention is that the RV and LV are paced independent of oneanother. This can be accomplished, for example, by triggering the LVpace/sense electrode pair (e.g., LV ring 25 and LV tip 26) based on asensed signal produced by the LV pace/sense pair, and triggering the RVpace/sense electrode pair (e.g., RV ring 34 and RV tip 32) based on aseparate sensed signal produced by the RV pace/sense pair. This meansthat the timing of at least a first pacing pulse (e.g., in a burst ofanti-tachycardia pacing pulses) is based on the corresponding sensedsignal. Timing of additional pulses (e.g., in the burst) can also bebased on the sensed signal. Alternatively, timing of additional pulsescan be based on a predetermined or calculated coupling interval. Thisshall now be explained in more detail with Reference to FIG. 3.

Referring to FIG. 3, waveform (b.) shows an exemplary sensed signal 312,picked up (i.e., sensed) by the LV pair, during tachycardia. Waveform(c.) shows an exemplary sensed signal 322, picked up by the RV pair,during the same tachycardia. In this example the location of thereentrant loop is closer to the LV pair than to the RV pair.Accordingly, as is apparent from waveforms (b.) and (c.), the reentrantloop is sensed sooner (i.e., earlier) at the LV pair. This embodiment ofthe present invention takes this into account when performing ATP. Morespecifically, rather than generating simultaneous right ventricle andleft ventricle pulses (i.e., simultaneous bi-ventricular pulses),independent LV pacing pulses and RV pacing pulses are generated, asshown by waveforms (d) and (e). Waveform (d) shows the a left ventriclepacing signal 332, for example, representing the voltage between LV ring25 and LV tip 26. Waveform (e) shows the right ventricle pacing signal342, for example, representing the voltage between RV ring 34 and RV tip36. In one embodiment, the coupling interval(s) of the LV pacing pulsesgenerated by the LV electrode pair are the same as the couplinginterval(s) of the RV pacing pulses generated by the LV electrode pair.Alternatively, the coupling interval(s) of the LV pacing pulsesgenerated by the LV electrode pair can be different than the couplinginterval(s) of the RV pacing pulses generated by the LV electrode pair.Thus each pacing pair does its independent sensing and pacing withoptimal timing.

These embodiments are further explained with reference to the flow chartof FIG. 4, which outlines a method 400 of the present invention that canbe implemented in an embodiment of device 10. In this flow chart, andthe other flow charts described herein, the various algorithmic stepsare summarized in individual “blocks.” Such blocks describe specificactions or decisions that are carried out as the algorithm proceeds.Where a microcontroller (or equivalent) is employed, the flow chartspresented herein provide the basis for a “control program” that may beused by such a microcontroller (or equivalent) to effectuate the desiredcontrol of the pacing device. Those skilled in the art may readily writesuch a control program based on the flow charts and other descriptionspresented herein.

Method 400 is used in response to the detection of a ventriculartachycardia. At a step 402 a a first signal (e.g., sensed signal 312) issensed in the heart's left ventricle. At a step 402 b (e.g., sensedsignal 322) a second signal is sensed in the heart's right ventricle. Ata step 404 a, first anti-tachycardia pacing pulses are delivered to theleft ventricle. The first time step 404 a is performed, timing of atleast one of the first pulses is based on the first sensed signal. At astep 402 b, second anti-tachycardia pacing pulses are delivered to theright ventricle. The timing of at least one of the second pulses ispreferably based on the second sensed signal. Notice that steps 402 aand 404 a are shown as occurring in parallel with, but independently of,steps 402 b and 404 b.

At a next step 406, there is a determination whether the ventriculartachycardia has been converted into normal sinus rhythm. If thetachycardia has been converted, then method 400 ends. If the tachycardiapersists (i.e., has not been converted to normal sinus rhythm), thenflow returns to steps 402 a and 402 b, as shown in FIG. 4. Accordingly,first and second sensed signals can again be produced (i.e., sensed),and used for timing additional anti-tachycardia pacing pulses.Alternatively, if the tachycardia persists, flow can return to steps 404a and 404 b, as shown in dashed line. The timing of additional pacingpulses can at this point be based on predetermined or calculatedcoupling intervals.

B. Pacing First with the Electrodes Closer to Reentrant Loop

According to an embodiment of the present invention, electrodes that areclosest to the reentrant loop are used first to attempt to convert aventricular tachycardia to normal sinus rhythm. This embodiment can beexplained with reference to the flowchart of FIG. 5, which outlines amethod 500 of the present invention that can be implemented in anembodiment of device 10. Method 500 is used in response to the detectionof a ventricular tachycardia. At a first step, 502, there is adetermination of which one of a first pair of electrodes (e.g., LV ring25 and LV tip) and a second pair of electrodes is closer to a reentrantloop of the ventricular tachycardia, where the first pair of electrodesare implanted in the left ventricle, and the second pair of electrodesare implanted in the right ventricle. Additional details of this stepare discussed below. For each of the embodiments discussed herein, it isnoted that “electrodes implanted in the left ventricle” is meant toinclude electrodes on the surface of the left ventricle, such as in theveins of the left ventricle.

At a next step 504, anti-tachycardia pacing (ATP) pulses are deliveredusing the pair of electrodes that are determined to be closer to thereentrant loop. According to one embodiment, ATP pulses are onlydelivered using the electrodes that are closer to the reentrant loop.

In an alternative embodiment, the other pair of electrodes (i.e., thosenot closest to the reentrant loop) are used to deliver ATP pulses if thetachycardia was not converted into normal sinus rhythm. Morespecifically, at a next step 506, there is a determination whether theventricular tachycardia has been converted into normal sinus rhythm. Ifthe tachycardia has been converted, then method 500 ends. If thetachycardia persists (i.e., has not been converted to normal sinusrhythm), then, at a step 508, anti-tachycardia pacing pulses aredelivered using the pair of electrodes that were not used at step 504.Next, at a step 510, there is another determination of whether theventricular tachycardia was converted into normal sinus rhythm. If thetachycardia as been converted, then method 500 ends. However, if thetachycardia persists than flow returns to step 504.

There are various ways that step 502 can be accomplished. Referring backto FIG. 3, in one embodiment, a first signal (e.g., 312) is sensed froma heart's left ventricle (e.g., using a pair of electrodes implanted inthe left ventricle), and a second signal (e.g., 322) is sensed from theheart's right ventricle (e.g., using a pair of electrodes implanted inthe right ventricle). The terms “first” and “second” as used herein arenot meant to signify an order (unless specifically specified to), butrather, are meant to distinguish signals sensed by different electrodes.These first and second sensed signals (e.g., 312 and 322) are offset intime from one another, as shown in waveforms (b) and (c), even thoughthey are sensing the same electrical activity. The reason these signalare offset from one another is due to the different distances theelectrodes are from the reentrant loop. The determination of which oneof the first pair of electrodes and the second pair of electrodes arecloser to the reentrant loop of the ventricular tachycardia can be basedon the first and second sensed signals (e.g., 312 and 322). For example,a corresponding pair of sensed pulses (e.g., 314 and 324) can becompared. It can be assumed that the pair of electrodes that sensed theearlier pulse (e.g., 314) of a corresponding pair or pulses (e.g., 314and 324) is the closer pair of electrodes (e.g., the left ventricularelectrode pair).

In another embodiment, in addition to sensing a first sensed signal(e.g. 312) and a second sensed signal (e.g., 322), a far field signal isalso sensed. Waveform (a.) of FIG. 3 shows an exemplary far field signal302 representing, for example, the voltage between RV coil 36 andhousing 40 (also known as the “can”, “case” or “case electrode”).According to an embodiment of the present invention, a determination ofwhether the reentrant loop is closer to the LV electrodes or RVelectrodes is based on far field signal 302. More specifically, if thebeginning of the far field pulse (i.e., the portion that begins to gopositive) is closer to an LV sensed pulse (e.g., of sensed signal 312),then it is assume that the reentrant loop is closer to the LVelectrodes. If the beginning of the far field pulse (i.e., the portionthat begins to go positive) is closer to an RV sensed pulse (e.g., ofsensed signal 322), then it is assume that the reentrant loop is closerto the RV electrodes. From exemplary waveforms (a), (b) and (c) of FIG.3, it can thus be determined that the reentrant loop is closer to theleft ventricular pair.

C. Unipolar Pacing

In another embodiment of the present invention, unipolar BV pacing isused. A potential problem with bipolar pacing is that the “reach” of theelectric field is relatively small because it is tightly confinedbetween the two electrodes of an electrode pair (e.g., the LV pair or RVpair). According to an embodiment of the present invention, the tip andring of one or more electrode pairs are shorted together, during pacing,to acts as a large unipolar pacing lead. For example, LV ring 25 and LVtip 26 are shorted together and/or RV ring 34 and the RV tip 32 areshorted together. In specific embodiments, when the LV ring 25 and LVtip 26 are shorted together to form a unipolar pacing lead, the returnelectrode(s) can be, for example: one of the RV ring 34 and RV tip 32;the can 40; or the RV ring 34 and RV tip 32 shorted together.

The shorting can be performed, for example, within the electrodeconfiguration switch 74. As mentioned above, electrode switch 74 can becontrolled by microcontroller 60, via control signal 80. The effectivelylarger lead (i.e., the lead produced by shorting together twoelectrodes) is less efficient and is probably not suitable for chronicpacing. However, in spite of its reduced electrical efficiency, theshorted unipolar pacing lead will stimulate many more cardiac cells,thereby increasing the chance of crossing through the wavefronts toterminate the tachycardia.

A shorted electrode pair of the present invention can be used for singleventricular pacing. Alternatively, shorted electrode pairs of thepresent invention can be used during simultaneous BV pacing (i.e., wherethe pacing pulse produced by the LV pair is synchronous with the pacingpulse produced by the RV pair). Alternatively, shorted electrode pairsof the present invention can be used during independent BV pacing of thepresent invention, which has been described above.

These embodiments can be explained with reference to the flowchart ofFIG. 6, which outlines a method 600 of unipolar pacing according to thepresent invention. Method 600 is used in response to the detection of aventricular tachycardia.

At a step 602, a sensed signal is produced based on a pair of electrodesimplanted in a ventricle. This can be the same sensed signal that wasused to detect the ventricular tachycardia, or this signal can be sensedafter the tachycardia is detected. The pair of electrodes are, forexample, RV tip electrode 22 and RV ring electrode 34. Alternatively,the pair of electrodes are LV tip electrode 26 and LV ring electrode 25.

At a next step 604, the pair of electrodes are shorted together, toessentially form a unipolar electrode. As mentioned above, the shortingcan be performed, for example, within the electrode configuration switch74 as controlled by microcontroller 60.

Then, at a step 606, anti-tachycardia pacing pulses are delivered to theventricle using the shorted together pair of electrodes. The first timestep 606 occurs following detection of a tachycardia, timing of at leastone of the pacing pulses (e.g., a first one of the pacing pulses) isbased on the sensed signal.

At a next step 608, the pair of electrodes are un-shorted. Onceun-shorted, the pair of electrodes can be used to detect the electricalcharacteristics in the heart. The un-shorted electrodes can then be usedto determine whether the tachycardia has been converted to normal sinusrhythm, at a step 610. Alternatively or additionally, another pair ofelectrodes can be used to determine whether the tachycardia has beenconverted to normal sinus rhythm.

If the tachycardia has been converted, then method 600 ends. If thetachycardia persists, then flow returns to step 602. If a signal wassensed to perform step 610, then steps 602 and 610 can be combined intoone step. Flow may alternatively return directly to step 604, as shownin dashed line.

In another embodiment of the present invention, more than two electrodesare shorted together at step 504. This will provide for an effectivelylarger unipolar electrode. For example, RV tip 32, RV ring 34 and RVcoil 36 can all be shorted together to produce an effectively very largeunipolar electrode. This very large unipolar electrode will stimulateeven more cardiac cells, thereby further increasing the chance ofcrossing through the wavefronts to terminate the tachycardia.

D. Unipolar BV Pacing with Leads of Opposite Polarities

A problem with unipolar pacing is that the current from the can to thepacing electrodes can result in pocket stimulation at the site of thecan (i.e., stimulation of muscle tissue surrounding the can). Pocketstimulation, although not dangerous, can be uncomfortable to a patient.In an embodiment of the present invention, pacing pulses generated by aunipolar LV electrode (e.g., produced by shorting together LV ring 25and LV tip 26) have an opposite polarity than pacing pulses generate byan RV unipolar electrode (e.g., produced by shorting together the RVring 54 and RV tip 52) when performing BV ATP. This would result in analmost zero net current flowing from the can, when the LV unipolarelectrode pulses and RV unipolar electrode pulses are deliveredsimultaneously.

In one embodiment, the polarity of each unipolar electrode is constantand opposite the other unipolar electrode. In another embodiment, thepolarity of a first unipolar electrode (e.g., produced by shortingtogether LV ring 25 and LV tip 26) alternates between a first polarity(e.g., positive) and a second polarity (e.g., negative), while thepolarity of a second unipolar electrode (e.g., produced by shortingtogether RV ring 54 and RV tip 52) alternates between the secondpolarity (e.g., negative) and the first polarity (e.g., positive) suchthat each unipolar electrodes always has the opposite polarity of theother unipolar electrode. In other words, opposite polarities are usedat different sites (e.g., the left ventricle and the right ventricle).The alternating could happen on a pulse by pulse basis. Alternatively,the alternating could happen on a pulse burst by pulse burst basis.

F. Multiple Pacing Configurations

According to an embodiment of the present invention, stimulation device10 is adapted to be able to perform ATP using a plurality of differentpacing configurations. Stimulation device can also be adapted toautomatically change pacing configurations. Exemplary different pacingconfigurations include: pacing only the right ventricle; pacing only theleft ventricle; and pacing the left ventricle and the right ventricle(i.e., bi-ventricular pacing). The bi-ventricular pacing configurationcan include simultaneously pacing the left ventricle and the rightventricle, or alternatively, independently pacing the left ventricle andthe right ventricle.

This embodiment can be explained with reference to the flowchart of FIG.7, which outlines a method 700 of changing pacing configurations. Method700 is used in response to the detection of a ventricular tachycardia.

At a step 702, ATP pulses are delivered using a first pacingconfiguration in response to sensing a ventricular tachycardia.

At a next step 704, there is a determination of whether the tachycardiahas been converted to normal sinus rhythm.

Then at a step 706, anti-tachycardia pacing is delivered using adifferent pacing configuration if it is determined, at step 704, thatthe tachycardia has not been converted to normal sinus rhythm.

According to an embodiment of the present invention, information isstored that identifies a pacing configuration that was used tosuccessfully convert the ventricular tachycardia to normal sinus rhythm,in response to determining that the tachycardia has been converted tonormal sinus rhythm. Then, in response to sensing another ventriculartachycardia, further anti-tachycardia pacing can be performed using thepacing configuration that was used to successfully convert the previousventricular tachycardia to normal sinus rhythm.

The above described method 700 can alternatively be thought of in termsof electrode configurations. That is, the method can be for changing theelectrode configuration used for anti-tachycardia pacing. Exemplaryelectrode configurations that can be used to deliver anti-tachycardiapacing pulses include electrodes implanted in the right ventricle;electrodes implanted in the left ventricle; and electrodes implanted inthe right ventricle and electrodes implanted in the left ventricle. Thismethod is for use in an implantable device capable of performing ATPusing a plurality of different electrode configurations. In a firststep, first ATP pulses are delivered in response to sensing aventricular tachycardia. The first ATP pulses are delivered using afirst electrode configuration. At a next step, there is a determinationwhether the tachycardia has been converted to normal sinus rhythm.Second ATP pulses are delivered using a different electrodeconfiguration if it is determined that the tachycardia has not beenconverted to normal sinus rhythm.

As mentioned above, in an embodiment of the present invention one of aplurality of pacing configurations (or electrode configurations) can beselected based on stored information. This will be explained in moredetail with reference to the flowchart of FIG. 8, which outlines amethod 800 of selecting a pacing configuration. This method, like method700, is for use in an implantable device capable of performinganti-tachycardia pacing using a plurality of different pacingconfigurations.

At a first step 802, a ventricular tachycardia is detected.

At a next step 804, one of the plurality of pacing configurations isselected, in response to detecting the ventricular tachycardia. Theplurality of pacing configurations can include, for example: pacing onlythe right ventricle; pacing only the left ventricle; and pacing the leftventricle and the right ventricle (i.e., bi-ventricular pacing).Bi-ventricular pacing can include, for example, pacing the left andright ventricles simultaneously, or independently pacing the left andright ventricles. This step is described in more detail below.

Next, at a step 806, ATP is performed using the pacing configurationselected at step 804.

According to an embodiment of the present invention, the pacingconfiguration that is selected at step 804 is the configuration that wasmost recently used to successfully convert a previous ventriculartachycardia to normal sinus rhythm.

According to another embodiment of the present, step 804 includes thesteps of: sensing a signal indicative of the detected tachycardia (e.g.,using a pair of electrodes); and selecting one of the plurality ofpacing configurations based on the shape (i.e., morphology) of thesignal. For example, the selection is of the pacing configuration thatwas used to successfully convert a previous ventricular tachycardiaassociated with a similar signal shape. This is very useful in treatinga heart that is susceptible to a tachycardia from different reentrantloops, each of which will produce a different signal indicative of thetachycardia. Selecting a pacing configuration that was previouslysuccessful to treat a tachycardia producing a similarly shaped sensedsignal should reduce the amount of time it will take to convert thetachycardia to normal sinus rhythm. Exemplary devices and methods formorphology discrimination are disclosed in U.S. Pat. No. 5,240,009(Williams) and U.S. Pat. No. 5,193,550 (Duffin), both of which areincorporated herein by reference.

According to an embodiment of the present invention, prior to step 802the following steps of are performed. First, morphology informationcorresponding to at least two previous ventricular tachycardia episodesare stored (e.g., in memory 94). Additionally, configuration informationthat identifies corresponding pacing configurations that were used tosuccessfully convert the at least two previous ventricular tachycardiasto normal sinus rhythm are also stored (e.g., in memory 94). Thisinformation can then be used to assist in the selection made at step804.

G. Adjusting Time Offset

According to an embodiment of the present invention, one a plurality oftime offsets between pacing pulses delivered in the right and leftventricles are selected. This embodiment, which is for use in animplantable device capable of performing bi-ventricular anti-tachycardiapacing (ATP), is described with reference to the flowchart of FIG. 9.

At a first step 902 of a method 900, a ventricular tachycardia isdetected. Once the ventricular tachycardia is detected, the remainingsteps of method 900 are performed. More specifically, at a next step904, a signal indicative of the detected tachycardia is sensed. If theventricular tachycardia is detected (at step 902) based on such a sensedsignal, then steps 902 and 904 can be combined into one step.

At a next step 906, one of a plurality of different time offsets isselected based on the shape of the sensed signal. Each time offsetdefines a delay between an ATP pulse delivered to the right ventricleand a corresponding ATP pulse delivered the left ventricle duringbi-ventricular ATP pacing. The time offsets can be positive or negative,to thereby specify which ventricle is paced first. For example, apositive time offset can specify that the right ventricle is pacedfirst, where a negative time offset can specify that the left ventricleis paced first. Of course, the present invention is not limited to thisexample.

At a next step 908, first ATP pulses are delivered to the rightventricle and second ATP pulses are delivered to the left ventricle,wherein each pulse in the second ATP pulses is offset in time from acorresponding pulse in the first ATP pulses by the selected time offset.The terms “first” and “second” as used herein are not meant to signifyan order (unless specifically specified to), but rather, are meant todistinguish ATP pulses delivered to different chambers.

According to an embodiment of the present invention, prior to step 902the following steps of are performed. First, morphology informationcorresponding to at least two previous ventricular tachycardia episodesare stored (e.g., in memory 94). Additionally, configuration informationthat identifies corresponding time offsets that were used tosuccessfully convert the at least two previous ventricular tachycardiasto normal sinus rhythm are also stored (e.g., in memory 94). Thisinformation can then be used to assist in the selection made at step906.

V. Conclusion

The previous description of the preferred embodiments is provided toenable any person skilled in the art to make or use the presentinvention. While the invention has been particularly shown and describedwith reference to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention.

Burst ATP pacing was mentioned above. However, the present invention isnot limited to use with burst ATP pacing. Rather, embodiments of thepresent invention can also be used with other types of ATP pacing, suchas, but not limited to, underdrive pacing, programmed extrastimuli (PES)and train pacing.

Many embodiment of the present invention can be combined. For example,the independent bi-ventricular ATP of the present invention can beperformed using unipolar pacing (i.e., shorted together electrodes) ofthe present invention. For another example, ATP pulses can be deliveredfirst to the electrodes that are closer to a reentrant loop, aftershorting together the electrodes to produce a unipolar pacing electrode.In still another example, ATP can be performed using a pacingconfiguration that was previously used to successfully convert anearlier tachycardia producing a sensed signal having a similarmorphology. The previous pacing configuration could be pacing the rightventricle using a unipolar electrode (e.g., produced by shortingtogether RV tip 32 and RV ring 34), pacing the left ventricle using aunipolar electrode (e.g., produced by shorting together LV tip 26 and LVring 25) or bi-ventricular unipolar pacing. These are just a fewexamples that are not meant to be limiting.

Furthermore, embodiments of the present invention discussed above havebeen primarily described as methods with reference to flow charts. Thepresent invention is also directed to devices (also referred to asapparatuses) that perform the features discussed above. For example, thepresent invention is also directed to a microprocessor (e.g.,microprocessor 60) that performs the features of the present invention.Additionally, the present invention is also directed to an implantabledevice (e.g., pacing device 10) that includes a microprocessor forperforming such features. Further, the present invention is alsodirected to systems that perform the features discussed above. Such asystem can be, for example, an external processor in communications witha microprocessor of an implantable device.

What is claimed is:
 1. For use in an implantable device capable ofperforming bi-ventricular anti-tachycardia pacing (ATP), a method forconverting a ventricular tachycardia to normal sinus rhythm, comprisingthe steps of: (a) detecting a ventricular tachycardia; (b) sensing asignal indicative of the detected tachycardia; (c) selecting one of aplurality of time offsets based on the shape of the signal; and (d)delivering first ATP pulses to the right ventricle and second ATP pulsesto the left ventricle, wherein each pulse in the second ATP pulses isoffset in time from a corresponding pulse in the first ATP pulses by theselected time offset.
 2. An implantable device capable of performingbi-ventricular anti-tachycardia pacing, comprising: means for detectinga ventricular tachycardia; means for sensing a signal indicative of thedetected tachycardia; means for selecting one of a plurality of timeoffsets based on the shape of the signal; means for delivering first ATPpulses to the right ventricle; and means for delivering second ATPpulses to the left ventricle, wherein each pulse in the second ATPpulses is offset in time from a corresponding pulse in the first ATPpulses by the selected time offset.